Note 3 - Loans and Allowance for Credit Losses on Loans (Details Textual) Pure in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2025 USD ($)	Mar. 31, 2024	Dec. 31, 2024 USD ($)
Financing Receivable, Accrued Interest, after Allowance for Credit Loss		$ 24,000,000		$ 23,000,000
Financing Receivable, before Allowance for Credit Loss	[1]	6,646,360,000		6,520,402,000
Loans and Leases Receivable, Related Parties		91,000,000		97,000,000
Financing Receivable, Nonaccrual, Interest Income		0		0
Mortgage Loans in Process of Foreclosure, Amount		$ 509,000		569,000
Financing Receivable, Modifications, Number of Contracts		0	0
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts		0	0
Asset Pledged as Collateral [Member] | Federal Home Loan Bank Advances [Member]
Financing Receivable, before Allowance for Credit Loss		$ 3,550,000,000		$ 3,480,000,000

[1] (1) Total loans are presented inclusive of premiums, discounts and net loan origination fees and costs.